The influence of electron cyclotron resonance heating on ion-driven fishbone instability

Abstract

The effect of electron cyclotron resonance heating (ECRH) on fishbone instability is studied based on the generalized energy principle. Off-axis ECRH plays a stable role on fishbone instability while on-axis ECRH do not distinctly change the growth rate. The frequency of fishbone instability increases (decreases) for off-axis (on-axis) ECRH. The effect of ECRH becomes largest when the power is deposited near the rational surface. More concentrated power deposition has a better stabilizing effect. Furthermore, the non-resonance effect of trapped energetic electrons (TEEs) is the main factor of stabilization effect in off-axis case, while it is weak in on-axis case. The frequency of fishbone instability is changed mainly by the Shafranov shift effect on trapped energetic ions (TEIs), since it can change the precessional drift frequency. The Shafranov shift effect can also affect the growth rate because the onset threshold of energetic ion beta is related to the frequency. The effects of magnetic Reynolds number and slowing-down critical energy are weak and can be neglected. This provides a possibility of using off-axis ECRH targeted to the rational surface to control fishbone instability.